In the past, atrial arrhythmias have been largely undertreated due to the perception that these arrhythmias are relatively benign. As more serious consequences of persistent atrial fibrillation have come to be understood, such as an associated risk of relatively more serious ventricular arrhythmias and stroke, there is a greater interest in providing implantable atrial or dual chamber cardioverter defibrillators for treating atrial arrhythmias.
Atrial fibrillation (AF) can be treatable with relatively high voltage defibrillation shocks, which are generally painful to the patient, or high frequency pulse bursts. Atrial flutter (AFL), also referred to herein as atrial tachycardia (AT) can be treated by anti-tachycardia pacing (ATP) therapies, pulse bursts or cardioversion shocks. Generally, it is preferred to initially treat AFL with a less aggressive therapy such as ATP, which is not painful to the patient and requires less battery energy than cardioversion shocks. Reliable discrimination between AFL and AF is important in selecting the appropriate atrial arrhythmia therapy and is also useful in monitoring a patient's arrhythmia disease status, managing medical therapy, and evaluating the effectiveness of arrhythmia therapies.
In AFL, the atria beat at an elevated rate that is highly regular, typically at 200 to 320 beats per minute. While beating at a pathologically high rate, the atrial contraction can be sufficiently coordinated to generate pressure within the atria. In AF, the atria depolarize at an elevated rate that can be regular or irregular. The atrial contraction is disorganized, however, and not efficient enough to generate pressure. AFL, characterized by a single depolarizing wavefront, is often treatable by anti-tachycardia pacing (ATP) therapies, whereas AF, characterized by multiple depolarizing wavefronts, is not treatable by ATP therapies.
Clinically, the efficacy of atrial ATP therapies is reportedly, on the order of less than 50%. This low efficacy rate may not reflect the effectiveness of atrial ATP therapies in successfully treating AFL, but instead reflect inappropriate AFL detections resulting in the delivery of atrial ATP therapies during a rhythm that is untreatable by ATP. If the rhythm is in fact AF, atrial ATP therapies will be ineffective. On the other hand, arrhythmias classified as AF that are in fact fast AFL may be unnecessarily treated with a more aggressive arrhythmia therapy such as a shock therapy, needlessly exposing the patient to shock pain and consuming battery energy. Improved specificity of atrial arrhythmia classification methods may therefore allow ATP therapy efficacy to be improved and conservative but appropriate use of defibrillation shock therapies.
Methods for specifically classifying atrial arrhythmias, for monitoring or therapy selection purposes, generally depend only on atrial rate information in current commercially available devices. Such information may include the atrial rate and the regularity of the atrial rate. A range of atrial rates may be specified for detecting AFL and a different, generally higher, range of atrial rates may be specified for detecting AF. However, because the atrial rate could be the same during AFL and AF, specified ranges for AFL and AF detection may overlap and therefore rate information alone is not always adequate for detecting and discriminating AFL and AF. When an atrial rate is detected in this overlap range, atrial cycle length regularity may be used for discriminating between AFL and AF. However, because the atrial cycle length can be regular during AF in some patients, atrial cycle length regularity may not always be a dependable distinguishing factor in discriminating AFL from AF either.
Therefore, what is needed is a method and device for discriminating between atrial arrhythmias when atrial rate information is ambiguous in discriminating AFL from AF.